Physicians make use of catheters today in medical procedures to gain access into interior regions of the body to ablate targeted tissue areas. For example, in electrophysiological therapy, ablation is used to treat cardiac rhythm disturbances. During these procedures, a physician steers a catheter through a main vein or artery into the interior region of the heart that is to be treated. The physician places an ablating element carried on the catheter near the targeted cardiac tissue, and directs energy from the ablating element to ablate the tissue and form a lesion. Such procedure may be used to treat arrhythmia, a condition in the heart in which abnormal electrical signals are generated in the heart tissue.
In certain procedures, it may be desirable to produce a deep lesion. For example, it may be desirable to produce a transmural lesion (lesion that extends the depth of a tissue) within ventricle tissue, because shallow or incomplete lesions may otherwise allow electrical signals to travel through the non-ablated tissue beneath the lesion. Therefore, it is believed that deep or transmural lesions can more efficiently block undesirable electrical paths. Because the ventricle tissue is thick, however, it may be difficult to create transmural lesions using the current technology.
An ablation procedure using a unipolar arrangement involves placing an indifferent patch electrode or a ground pad on a patient skin. Ablation energy is directed from another electrode (the ablating electrode) placed against the target tissue, while the indifferent patch electrode is electrically coupled to a ground or return input on the radio-frequency generator, thereby completing the energy path. In this case, ablation energy will flow from the ablating electrode to the patch electrode. One of the disadvantages of this procedure is that much of the RF energy is dissipated or lost through intervening organs, tissues, and/or blood pool between the ground pad and the target tissue that is being ablated. As the result, it is more difficult to ablate tissue below the surface of the target site using current unipolar arrangements.
An ablation procedure using a bipolar arrangement involves using an ablation catheter that carries two electrodes. In this case, ablation energy will flow from one electrode (the ablating electrode) on the catheter to an adjacent electrode (the indifferent electrode) on the same catheter. Because both the ablating electrode and the indifferent electrode are usually located on one side of the tissue to be ablated, some of the ablation energy delivered by the ablating electrode may only affect tissue that is closer to the surface of the target site, and may tend to return to the indifferent electrode without substantially affecting deeper tissue. As a result, it is more difficult to ablate tissue below the surface of the target site using current bipolar arrangements.
Another problem associated with current ablation devices is that during an ablation procedure, a return electrode used for returning energy to an ablation source may heat up. In the unipolar arrangement where the return electrode is placed in contact with a patient's skin, the overheating of the return electrode may cause injury to the patient's skin. In the bipolar arrangement where the return electrode is placed within the body and adjacent to the ablating electrode, the overheating of the return electrode may cause internal healthy tissue that is in contact with the return electrode to be unnecessarily heated.
Furthermore, ablation of heart tissue poses another challenge in that the heart is constantly moving during an ablation procedure. As a result, it is difficult to maintain stable contact between an ablating or ground electrode and the constantly moving target tissue.
Thus, there is currently a need for an improved ablation device and method for creating lesions.